MANGAN, India (AP) — Indian soldiers in helicopters and driving heavy road clearing equipment scrambled Wednesday to reach a hydroelectric project in northeast India where at least a dozen people died and scores more were missing after a powerful earthquake.

The 6.9 magnitude earthquake Sunday evening killed at least 91 people across northeast India, Tibet and Nepal. Rescue efforts have been hampered by heavy rain and mudslides that blocked the roads leading to isolated villages.

The quake triggered a landslide that buried the workers’ quarters at a hydroelectric plant being built along the Teesta River in the town of Saffo in the northern part of the Indian state of Sikkim, said Jigmee Bhutia, an official with Teesta Urja Co., which is building the plant.

Bhutia said at least 12 workers were killed and at least 40 others were missing after the quake.

Soldiers in helicopters tried to get to the area while other rescue workers used heavy machinery to try to clear the roads, local official Janim Lepcha said.